Thermal protective system



Jan. 5., 1937. M. w. BARTMESS 2,066,904

THERMAL PROTECTIVE SYSTEM Filed Dec. 12, 1954 2 Sheets-Sheet 2 Ill HI NHfig.- 6 4/ 85 l m WITNESSES: 49 INVENTOR ATTORNEY Patented Jan. 5, 1937UNITED STATES PATENT, OFFICE THERMAL rnornc'rrvn SYSTEM Pennsylvania-Application December 12, 1934, Serial No. 757,141

'iclaims.

My invention relates to protective systems and particularly to overloadprotective systems for polyphase electric motors.

An object of my invention is to provide a relatively simple method forprotecting a polyphase alternating-current motor against excessivetemperature rise.

Another object of my invention is to provide a thermal protective systemfor a polyphase alternating-current motor, embodying a plurality ofseparate control elements.

Another object of my invention is to provide a thermal protective systemfor a polyphase alterhatingcurrent motor that shall be actuatedinitially in accordance with the temperature of the motor and then'inaccordance with the effect of an extra overload current in a certainphase circuit of the motor.

Other objects of my invention will either be specifically pointed outhereinafter or will be evident from a description of a method and'systemembodying my invention, now preferred by me.

In practicing my invention, I provide, in combination with a polyphasealternating-current electric motor, a thermal relay mounted in directheat-receiving relation with either the frame or the stator winding andalso a current-controlled switch which may be operatively mounted on themotor or may be remotely located therefrom.

In the drawings:

Figure 1 is a view, mainly in front elevation but with parts brokenaway, of a polyphase electric motor having associated therewith thecontrol switches used in my invention;

Fig. 2 is a schematic diagram of connections of one system of electriccircuits used in practicing my improved method;

Fig. 3 is a diagram of connections showing a Fig. 6 is a diagram ofconnections similar to Fig. 3 but applied to a two-phase motor.

Referring first to Fig. 1 of the drawings, 1 have there illustrated,more or less generally only, an

electric motor having a .housing l3, 9. set of stator laminations l5secured therein and provide-d also with two bearing brackets or endbells l1 and I9 held against the housing by bolts 20.

As the method embodying my invention has first been worked out andapplied to, an explosionresisting motor, I have illustrated generally. amotor of this type, but my invention not limited to such motors but maybe used on any polyphase alternating-current motor. The motor includesalso a polyphase energizing stator winding designated by the numeral 2|in Fig. 1 of the drawings and shown as comprising windings 23, and 21(see Fig. 2-) which for illustrative purposes are shown as beingconnected in star.

The motor includes further a rotor 29 which may be of the squirrel-cagetype and include a rotor shaft 3|.

Bearing bracket I9 is provided with an extension 33 thereon having acover 35 associated therewith and adapted. to be bolted thereagainst toprovide a switch chamber 31 having located therein acircuit-interrupting device 39, which is manually closable as by a leverarm 4| and which is automatically actuable to open-circuit position, aswill be hereinafter more fully set forth. In order to actuate arm 4| toclose the circuit-breaker, I provide an external actuating arm 43mounted on a stud 45 extending through the cover 35 and provided withany suitable or desired type of arm 41 to engage switch arm 4| andactuate it to close circuit-breaker 39 when desired.

A thermal relay 49 is mounted in direct heatreceiving relation in thehousing I3 and more particularly in a recess in the bearing bracket l9and includes a base 5| suitably tightly clamped against the innersurface of bearing bracket I9 as by a plurality of short machine screws53.

Device 49 includes also a snap-acting bimetallic disk 55 which may be ofthe kind disclosed and claimed in patent No. 1,448,240 to J. A. Spencer.A plurality of contact members 51 are insulatedly mounted on andsupported by'the disk 55 adjacent to its periphery and cooperate withsubstantially fixed contact members 59 supported in an insulated manneron the base 5|. The design and construction of device 49 is such as toprovide a plurality of cooperating contact members which are disengagedfrom each other when the disk 55 is heated to a certain temperature,when it will move with a snap action from the position shown in Fig. 1of the'drawings to an oppositely dished position (shown by the brokenlines in Fig. 2) whereby disengagement of the normally engaged contactmembers is effected to thereby interrupt an energizing circuit in whichthe relay is electrically connected.

The disk 55 is supported on a stud 6| which has screw-threadedengagement with base 5| and may be located in an adjusted position by alocking nut 63, all in a manner nowwell known in the art. Device 49includes also a -small-heating ele: ment 65 which is so connected withcertain of the fixed contact members 59 as to be traversed by the samecurrent as traverses the circuit in which the thermal switch 49 isconnected and which it there illustrated schematically the circuitconnections for energizing the three-phase windings 23, 25 and 21 of astar-connected polyphase motorenergizing winding (the rotor having beenomitted for the sake of clearness). The supply of electric energy, at asuitable voltage, is through three supply-circuit conductors L1, L2 andL3 and I have illustrated schematically one form which switch 39 maytake. Thus it may comprise two pivotally mounted switch blades 81 and 69whose movable ends are secured respectively to a plate ii ofelectric-insulating material, the movable ends of arms 61 and 59cooperating with substantially fixed contact members 13 and I5. Theswitch arms may be moved manually by means (not shown in the drawings)to the closed position where they are held by a bimetallic latch 11which is connected in circuit with one of the blades as, for instance,blade 69, to be traversed by the same current as is carried by thisswitch blade. It may here be stated that the schematic showing or device39 in Fig. 2 of the drawings is very general only and that I may use,for instance, a device of the kind disclosed and claimed in Patent No.1,726,233 to H. K. Krantz and assigned to the same assignee as is thepresent application.

Let is be assumed that the motor H has been operating at either normalload or at variable loads which have not been excessively large orbeyond the normal rating of the motor, but that the load increases to arelatively large overload value whereby a temperature rise of the motoris caused, and let it be assumed further that this temperature risereaches a value which would in a short time become dangerous to theinsulating material used in the motor. I prefer to make thecurrent-carrying capacity of thermal switch 49 slightly less than thatof switch 39, although this is not an essential element 0! my invention.If the normal capacity of switch 49 is slightly less or, in other words,it it is set to interrupt its circuit at a temperature slightly lessthan that at which switch 39 will operate and if this temperature isreached in switch 49, it will open, the disc moving to the positionshown by the broken lines. The energizing circuit from supply circuitconducor L: is thereby interrupted and the motor I I will continue tooperate as a single-phase motor with, of course, greatly increasedcurrent-traversing the two windings 23 and 21. and supplied Iromconductors L1 and L2. The effect of the current traversing the bimetalmember 11 of substan-' tially U-shape, is such that its free end willmove outwardly away from under the plate ll so that the movable parts ofthe switch will be permitted to move to open position whereby the supplyof energy to the two-phase circuits of the motor will also beinterrupted. "After both switches have operated, the motor is entirelydeenergized and is also completely disconnected from the energizingcircuit. While thermal switch 49 will reclose after its temperature andthat of the motor have decreased, this will not be sufllcient to restartthe motor, since connection is thereby made to only one. terminal of oneof the phase windings. n order to restart the motor, it is necessary toeflect reclosure or switch39, as by means or the actuating arm 43. I,wish to here point out that there exists a diflerence in the operationof switch 49 and oi.- switch 39, namely, that the operation of switch 49is by thermal effect alone, while the operation or switch 39 may beconsidered as being primarily caused by current action, that is, thecurrent traversing bimetal element 71' causes it to operate to effect orpermit opening of the switch.

Referring now to Fig. 3 of the drawings, I have there illustrated amodified form of system embodying my invention and shown as beingapplied to the same motor as was hereinbefore described in connectionwith Figs. 1 and 2 of the drawings. Instead of using acircuit-interrupting device 33 depending for its operation upon theheating effects of a current, I use an overload circuit breaker actuatedsolely and directly in accordance with an excess current. I haveindicated a circuitinterrupter 8| which may have cooperating fixed andmovable contact members to control two separate circuits. It may furtherincludean overload coil 83 cooperating with a movable core 85 associatedwith the other parts of circuit-breaker 8|, so that upon the passage ofan overload current or a predetermined value through 0011 83, it willoperate to move the circuit-breaker to open position, where it willremain until manually reclosed by an actuating handle 81. While therewill be some time lag in the thermal electric device 39, shown in Figs.1 and 2 of the drawings, there will be substantially no delay in theoperation of device 8| since it depends upon the magnetic effect of anexcess current. The single pole thermal switch 49 hereinbeiore describedis used also in this circuit. The operation of the system shown in Fig.3 is substantially the same as that described hereinbefore in connectionwith Fig. 2 or the drawings. It may be noted that the circuit-breaker 9|maybe located away from the motor, as, for instance, on a switchboard ora control panel, if desired.

Referring now to Fig. 4 o! the drawings, I have there illustrated theapplication of my method voif limiting the temperature rise of a motoras applied to a two-phase alternating-current motor having phasewindings 9| and 93. A single pole thermal switch l9 may be connected incircuit with phase winding 93, which may be energized from supplycircuit conductors La and L4 01' the usual two-phase supply circuit. Theparts of thermal switch 39 may be the same as to design as that shownand described in Fig. 2 of the drawings so that no further descriptionthereof is believed to be necessary.

If an overload occurs on the motor comprising the energizingwindings 9|and 93, the thermal switch 49 will operate to interrupt its circuit,whereby the motor will be caused to operate as a single-phase motorenergized from conductors L1 and Lo. The resulting temperature rise inbimetal latch 11 will cause it to move in a manner well known in the artto the right to permit openelectric motor will be entirely deenergized,I may use the system illustrated in Fig. 6 of the drawings. I make useoi. a three-pole circuit-breaker ifli which is, in general, of the sameconstruction and which embodies the same principles of operation as thebreaker 8 l, except that it embodies three sets of cooperating contactmembers, which are connected in the leads L1, La and L3. The thermalswitch 49 is connected in lead L4. It will be noted that the actuatingcoil 93 is connected in lead L3, that is, in circuit with phase winding9|.

In case of an excessive temperature rise in the motor,the single polethermal switch 49 will be caused to open, causing the motor to operateas a single-phase motor with a. greatly increased current valuetraversing phase winding 9|. This excess current causes opening of thebreaker llll, whereby both phase windings are fully deenergized. Even ifthermal switch 49 does reclose, upon cooling of the motor, neither ofthe two phase windings will be reenergized, since only one terminal ofone phase winding is connected to a source of voltage.

Referring now to Fig. of the drawings, I have there illustrated ahousing 13, stator laminations l5 and a polyphase winding 2|, togetherwith a rotor 29. I have illustrated also a modified form of the thermalswitch 49 which I have indicated by the numeral 95 and which may be ofthe kind disclosed and claimed in United States Patent No. 1,947,078 toH. E. Cobb. In this form of a thermal switch, .the same type ofsnap-acting disk having contact members associated therewith, a base forsupporting the disk and also for supporting cooperating fixed contactmembers is provided, and

the operation of this device is the same as that hereinbefore set forthfor thermal switch 49.

If it is not desired to use the construction and location of switch 49as shown in Fig. 1 of the drawings, the thermal switch 95, as shown inFig. 5 of the drawings, may be used and be mounted directly on theenergizing winding, and it will be obvious that this may result inbetter protection of the motor because of the fact that the thermalswitch 95 is located close to the copper of the motor.

The location of switch 95 in direct'heat-receiving relation with thestator energizing windings 2| has the further advantage that there is asmaller temperature differential between the copper and the thermalswitch, so that it may be expected that this switch 95 will follow moreclosely the temperature variations of the energizing or phase windingsand thereby better protect the motor against possible excessivetemperature rises and burnouts because of relatively large overloadsthat are continued for too long a ,period of time.

It will be noted that the method embodying my invention provides onecontrol device which is purely thermally controlled or actuated, whilethe second control deyice may be said to be current controlled. It isfurther obvious that it is not necessary that the current controlledcircuit interrupter be located closely adjacent to or inside of themotor frame, since it is not dependent directly upon thetemperature riseof the motor, but depends more particularly upon current effects.

The method embodying my invention thus provides means for interruptingone phase circuit of a plurality of such circuits, thereby overloadingthe other phase circuit or circuits, the increased current traversingsuch circuits being then' operative to cause actuation of acurrent-controlled parting from the spirit and scope thereof, and Idesire, therefore, that only such limitations shall be placed thereon asare imposed by the prior art or are set forth in the appended claims.

I claim as my invention:

1. In combination with a polyphase electric motor comprising a statorand polyphase windings thereon, a switch thermally responsive to a partof said motor for controlling the energization of one of said windings,and a current-controlled switch dependent upon the opening operation ofsaid first-named switch for controlling the energization of the otherwindings.

2. In combination with a polyphase electric motor comprising a statorand polyphase windings thereon, a switch, responsive to the temperatureof a part of said motor, mounted on the stator and controlling theenergization of one of said windings, and a plural-pole current-actuatedswitch dependent upon the opening operation of said first-named switchfor controlling the energization of the other windings.

3. In combination with a polyphase electric motor comprising'a statorand polyphase windings thereon. a single pole thermally-actuable switchon the stator adapted to open the energizing circuit of one of saidpolyphase windings when the stator temperature reaches a certain valueand a plural-pole current-actuated switch adapted to interrupt theenergizing circuit of the other polyphase windings in response to excesscurrent conditions therein.

4. In a motor-protecting system, the combination with an electric motorcomprising a polyphase energizing winding, of a thermally-actuableswitch responsive to motor temperature and controlling one phasecircuit, and a current-actuated switch dependent upon the openingoperation of said first-named switch for controlling the other phasecircuits.

5. In a motor-protecting system, the combination with an electric motorcomprising a polyphase energizing winding, of a single-pole thermalswitch located in heat-receiving relation to the motor and controllingone phase circuit, and a plural-pole current-actuated switch dependentupon the opening operation of said first-named switch for controllingthe other-phase circuits.

6. In a protecting system for an electric motor having a polyphaseenergizing winding and a plurality of energizing leads connectedthereto, a single-pole thermally-actuable switch located inheat-receiving relation to the motor and connected in one only of saidenergizing leads, a plural-pole current-controlled switch connected in aplurality of energizing leads and means directly thermally associatedwith the single pole switch to cause the operation thereof inpredetermined sequence relatively to the plural-pole switch.

7. In a protecting system for an electric motor having a polyphaseenergizing winding and a plurality of energizing leads connectedthereto, a single pole thermally-actuable switch located inheat-receiving relation to the motor and connected in circuit with oneonly of the energizing leads, a plural-pole current-controlled switchconnected in circuit with a plurality of energizing leads, and acurrent-traversed heating element in heat-transferring relation to thesinglepole switch to cause the operation thereof before the plural-poleswitch is operated.

MEIGS W. BAR'I'MESS.

